Joining of dissimilar materials using impact welding

ABSTRACT

A system and method for joining dissimilar metals. In one embodiment, a method comprises providing a first metal plate, a second metal plate, and an intermediate body that is positioned between the first metal plate and the second metal plate. The first metal plate is then driven into the intermediate body, which causes at least a portion of the intermediate body to collide with the second metal plate. As a result, the material of the intermediate body joins the first metal plate to the second plate. In another embodiment, a method for joining dissimilar metals comprises providing a first metal that is not amenable to welding, a second metal that is joinable to the first metal, and an intermediate body that is not joinable to at least the first metal. The intermediate body may have at least one hole such that the first metal and the second metal are positioned over and on opposite sides of the hole(s). At least a portion of the second metal may then be driven into the hole(s) to be joined to first metal.

This application claims the priority benefit of U.S. ProvisionalApplication No. 62/532,336, filed Jul. 13, 2017, which is herebyincorporated by reference in its entirety.

BACKGROUND AND SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention relate to the field ofimpulse metalworking. Specifically, new devices and methods forimpact-driven joining are described that allow dissimilar materials tobe joined. Other aspects and advantages of the present invention will beapparent from the descriptions and drawings of exemplary embodiments.

When a sheet of metal is accelerated to very high speed and an obstacleis placed in its path, then because of its inertia, it would conforminto or around that obstacle. Hence the sheet forms into a certain shapeif the obstacle is in the form of a female die, or shears if theobstacle is a sharp edge. It is also well known that collision of a fasttravelling piece of metal with another can lead to a weld, if the impactvelocity and angle are in an optimum range. Collision welds aregenerally observed when the impact velocity is in the range of 150 m/sto 500 m/s and the impact angle is between 5 to 20 degrees.

Impulse metalworking has some distinct advantages over traditionalquasi-static methods. Impulse forming leads to lower spring back, higherformability and can be implemented with single sided tooling. Impactwelding has been shown to result in welds which are stronger than theparent materials. It is a solid state welding process with little or noheat affected zone because of which brittle intermetallics do not form.This process is widely used for joining dissimilar metals which are verydifficult, sometimes impossible, to join by traditional fusion weldingprocesses. The two most common agents for driving the metallic workpieceto high velocities are electromagnetic forces and explosives.

The electromagnetic launch of the workpiece is based on laws ofelectromagnetic induction and Lorentz forces. When a conductor,considered as a secondary coil, is placed in proximity to anotherconductor, considered as a primary coil, carrying a transient current,then a current opposing the change in magnetic field is induced in theformer. These conductors carrying opposite currents repel each other andhence the workpiece gets accelerated to a high velocity. The primarycoil is generally insulated from the workpiece by encapsulating it in anepoxy matrix. If the cycle times are low, the joule heat developedduring the process can melt the epoxy material, leading to currentshortage. There are also pressure limitations on the primary coil whichdepend on the mechanical strength of the epoxy as well as the coilmaterial. Hence, the application of electromagnetic forming is limitedat high energies and large numbers of operations by the availability oflong-lived electromagnetic coils. In addition, the workpiece either hasto be electrically conductive, or it has to be driven by a conductiveflyer.

Use of explosives for forming or welding has problems of its own. Theirsafe implementation in closed industrial settings is difficult. Also,they are mostly used for only large scale applications, and there is ahigh expenditure on infrastructure. Also, there are government and OSHAregulations which limit the use of explosives.

With the proliferation of small electronic devices, it is oftennecessary to join surfaces that are too thin or too sensitive to heatfor conventional means of metal-joining or welding. One example of thisis a mobile communications device.

It is therefore an unmet goal of the prior art to provide a reliablemethod of joining components, especially when there are dissimilarmetals or non-metallic composites involved and/or thin or sensitivematerials involved.

At least one of these unmet goals may be met by the exemplary methodsand devices described in more detail below. In one exemplary embodiment,a method for joining dissimilar metals comprises providing a first metalplate, a second metal plate, and an intermediate body that is positionedbetween the first metal plate and the second metal plate. Theintermediate body may be comprised of a material that is amenable to bejoined to the first metal and the second metal. The first metal plate isthen driven into the intermediate body, which causes at least a portionof the intermediate body to collide with the second metal plate. As aresult of the collision, the material of the intermediate body joins thefirst metal plate to the second plate.

In another exemplary embodiment, a method for joining dissimilar metalscomprises providing a first metal that is not amenable to welding, asecond metal that is compatible to be joined to the first metal, and anintermediate body that is not amenable to being joined to at least thefirst metal. In this example, the intermediate body may have at leastone hole such that the first metal and the second metal are positionedon opposite sides of the intermediate body and over the at least onehole. At least a portion of the second metal may then be driven into thehole(s) such that the second metal is joined to the first metal.

In addition to the novel features and advantages mentioned above, otherbenefits will be readily apparent from the following descriptions of thedrawings and exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be had when reference ismade to the accompanying drawings, wherein identical parts areidentified by identical reference numerals and wherein:

FIG. 1 is a schematic of an exemplary embodiment of a vaporizing foilactuator system;

FIG. 2 is a perspective view of the exemplary embodiment of theintermediate body of the vaporizing foil actuation system shown in FIG.1;

FIG. 3 is a perspective view of a second exemplary embodiment of anintermediate body that may be used in a vaporizing foil actuationsystem;

FIG. 4 is a perspective, partial section view of a third exemplaryembodiment of an intermediate body that may be used in a vaporizing foilactuation system;

FIG. 5 is a top perspective view of the intermediate body of FIG. 4,which indicates a cross-section line 4-4;

FIG. 6 is a schematic of an exemplary embodiment of a vaporizing foilactuation system comprising an intermediate body that has a hole tofacilitate welding, which indicates a cross-section line 7-7, whereinthe intermediate body may not be amenable to welding (a vaporizing foilactuator is not shown for clarity);

FIG. 7 is a cross-sectional schematic of the vaporizing foil actuationsystem of FIG. 6 (showing a vaporizing foil actuator);

FIG. 8 is a schematic of an exemplary embodiment of a vaporizing foilactuation system comprising an intermediate body that has multiple holesto facilitate welding, which indicates a cross-section line 9-9, whereinthe intermediate body is not amenable to welding (a vaporizing foilactuator is not shown for clarity); and

FIG. 9 is a cross-sectional schematic of the vaporizing foil actuationsystem of FIG. 8 (showing vaporizing foil actuators).

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

U.S. Pat. No. 9,021,845 describes the technique of rapidly vaporizing aconsumable body, especially of metal, to cause a piece of metal,generally referred to as the flyer, to accelerate and collide with atarget, resulting in a joining of the respective pieces.

In many embodiments of a system and method of the present invention, theconsumable body may comprise a metal foil, although many other forms ofmetal, such as wire, mesh, etc., are deemed useful for this purpose.

In one embodiment of a system and method, the stationary body may be adie, such that a piece of sheet metal may be deformed by the collisionto create a desired shape or surface structure. In another embodiment ofthe method, the stationary body may be a die that contains holes, suchthat the piece of sheet metal may be perforated or sheared by thecollision to create a desired hole or series of holes.

In a yet another embodiment of a system and method, the stationary bodymay be a further piece of metal, such that the piece of sheet metal maybe welded thereto by the collision. In this type of embodiment, thepiece of sheet metal and the further piece of metal may be dissimilarmetals. Also, the further piece of metal need not be stationary. In somesituations, using two vaporizing foils to accelerate the respectivepieces of metal into a collision with each other may create better weldsthan if one piece is stationary. This “dual acceleration” technique maybe more difficult to implement than a single foil method, but mayprovide sufficient advantage in the correct circumstance.

In any of these systems or methods, the piece of sheet metal may attaina velocity of at least about 200 m/s, although the velocity window forachieving impact welding may be quite large and velocities in the rangeof 2000 m/s during the accelerating step may be possible.

In many embodiments, aluminum, as well as its alloys, may be the metalfoil in the consumable body.

When preparing the consumable body, some embodiments may furthercomprise a layer of an unstable energetic chemical mixture. This may be,for example, an oxidizer fuel mixture or an unstable compound such asnitromethane. One exemplary unstable energetic chemical mixture maycomprise kerosene oil and potassium chlorate. It is also possible insome situations to add a layer of a polyurethane elastomer to theconsumable body, preferably on a face that is directed towards the pieceof sheet metal to be accelerated. Such a polyurethane layer may be usedwith or without the unstable energetic chemical mixture.

In other embodiments, the consumable body may comprise two layers ofmetal foil or mesh, with an intermediate layer of the unstable energeticchemical mixture.

In an exemplary embodiment, the vaporizing of the consumable body may beachieved by passing a high current rapidly into the foil, particularlyby discharging a capacitor or a bank of capacitors.

In many of these methods, the consumable body, the piece of sheet metaland the stationary body may be arranged in that order between a pair ofblocks of metal, each of which may significantly outweigh the piece ofsheet metal, thereby directing the vaporized stream towards the piece ofsheet metal and accelerating the piece of sheet metal towards thestationary body. In some exemplary embodiments, a target sheet may bebacked (e.g., immediately backed) by a layer of material that may serveas a dampener during the impact process. One example of a dampener layermay be comprised of a thin layer of a relatively soft material that haslow stiffness and density.

Turning now to an example of a specific application, there aresituations where two dissimilar metals are to be joined. By using avaporizing foil actuator in combination with an intermediate body thatis especially selected and shaped for the application, 100% jointefficiency has been demonstrated. Of course, it will be clear to one ofskill that the technique described may be used in many situations whenthe metals are similar, but the joining of similar metals may also beaccomplished by methods that are not applicable to dissimilar metals, soall mention here is to “dissimilar” metals.

In an example of the technique, one of the dissimilar metals is selectedto be the flyer plate and the other to be the target. A gap between thetwo sheets may be created by preforming or pre-machining one or both ofthe sheets or inserting one or more standoff bodies (e.g., sheets,washers, etc.) between the sheets of dissimilar metal. Size, shape, andmaterial may all be factors to be considered in making the selection.FIG. 1, as an example, shows a top plan view of two sheets 10, 12, ofdissimilar metals, with sheet 12 designated as the target plate andsheet 10 designated as the flyer plate. In other exemplary embodiments,as aforementioned, the metals may be similar.

At this point, the intermediate body 14 can be determined. In thisembodiment, since the action of a vaporizing foil actuator 16 onto flyerplate 10 is to drive a portion of the flyer plate into the intermediatebody 14, and, as a result of this primary collision, to accelerate atleast a portion of the intermediate body into the target plate 12, theintermediate body needs to be a material that is amenable to beingjoined to each of the dissimilar metals, even though the dissimilarmetals may not be amenable to direct bonding to each other.

Beyond selection of the material for intermediate body 14, it is alsobelieved to be important to consider the shape thereof. One example of apreferred intermediate body 14, as presently understood, is athree-dimensional body, shaped to facilitate the movement of metalwithin the intermediate body 14, initiated by the vaporizing foilactuator in a manner that allows the overall thickness of theintermediate body to be reduced by the bonding process.

A first example of such an intermediate body 14 is shown in FIGS. 1 and2, where the intermediate body is seen in elevation and perspectiveviews, respectively. In this embodiment, the intermediate body 14 has an“H” shape profile in the thickness dimension. The upright arms 22 of the“H” provide spacing between the flyer plate 10 and the target plate 12.The crossbar 24 that joins the upright arms 22 provides an intermediateplate that is impacted, preferably towards a central portion, by theflyer plate 10. This results in the crossbar portion being driven inturn into the target plate 12.

A variation of this concept may be to use an intermediate body with an“X” shaped profile. This shape may provide the advantage of starting theprocess of reducing the thickness of the body, or, stated slightlydifferently, moving the flyer and target plates into closer proximity. Apossible disadvantage of this shape in some circumstances is that it maycause more distortion of the flyer and target plates, and it also maynot provide an adequate target into which the accelerated flyer platemay collide.

Building on this concept, a variation of the intermediate body 114 isshown in a perspective view in FIG. 3. In this embodiment, which is ahybrid between the “H” profile of FIG. 2 and an “X” profile that lacks acrossbar, a pair of bent upright arms 122 are joined with a crossbar 24,so that the upright arms intersect the crossbar at an obtuse angle,rather than at a right angle. As such, upright arms 122 may beconsidered to form a V shape in this embodiment. This combination ofcrossbar 24 with upright arms 122 carries forward the impact area of thecrossbar, whereas the bent upright arms facilitate the compression ofthe intermediate body 114 in the direction of the impact.

In any of the foregoing examples, a rectangular (and probably preferablysquare) profile is provided to the target and flyer plates, that is,normal to those plates.

A further variation may be to change the rectangular profile into acircular profile. In some embodiments, a disc with uniform thickness maynot provide the requisite spacing. In other embodiments, a torus, withan open center, may lack the desired mass to be driven forward by theflyer plate into the target plate. As a result, it may be preferred tohave a disc 214, such as is shown in a perspective, partial section viewin FIG. 4 and in a top perspective view in FIG. 5. The intermediate body214 has at least a minimum thickness across its diameter, but, movingfrom a central axis outwardly, the thickness may increase and thendecrease, preferably in a smooth manner. Such a body 214 may be expectedto expand in diameter, displacing metal outwardly during the joiningprocess.

In another exemplary method of using vaporizing foil actuation to joindissimilar materials, one of the materials may be a material that is noteven subject to welding. An example may be a sheet of a carbon fibercomposite, which cannot be joined to a metal by welding.

Such as shown in the example of FIGS. 6 and 7, one way of practicingthis method is to provide a first metal sheet 310, the sheet that is tobe joined, but which may not be amenable to welding, and a second metalsheet 312, which is compatible to being joined to the first metal sheet310. For purposes of the description, the sheet 314 which is notamenable to welding will be referred to as the non-weldable sheet. Itcould, however, also be a metal sheet of a material that is notcompatible for welding onto the first metal sheet 310. Other types ofmaterial that are not subject to welding may also be used. In anexemplary embodiment, one or more holes 320 may be made, by drilling orother technique suitable to the material, in the non-weldable sheet 314,preferably near, but spaced away from, a margin or edge where the sheet312 is to be joined to the first metal sheet 310. Preferably, thenon-weldable sheet 314 and the first metal sheet 310 are held in placerelative to each other, with a portion of the first metal sheet 310overlying or covering each of the one or more holes 320 in thenon-weldable sheet 314. In an exemplary embodiment, the first metalsheet 310 may be arranged such that the area where the sheet 310overlies the one or more holes 320 in the non-weldable sheet 314 is alsonear but spaced away from a margin or edge where the first metal sheet310 is to be joined to the sheet 312. In another exemplary embodiment,it will also be recognized that the one or more holes 320 may be in, andoverlap an edge of, the non-weldable sheet 314, so that the two metalsheets 310, 312 may be joined through the hole or holes in a manner thattraps the non-weldable sheet in place.

The second metal sheet 312 is also positioned to overlie or cover atleast one of the one or more holes 320 in the non-weldable sheet 314, onthe side opposite the first metal sheet 310. In many instances, thissecond sheet 312 is serving only as a fastener, so it may bespecifically sized and shaped for that purpose, such as by centering thesecond sheet 312 over the one or more holes 320. In some instances, forexample, the second sheet may be a circular disc, centered over a holein the non-weldable sheet. A variety of techniques, including forillustrative purposes and not for limitation, clamping or adhesive, maybe used to hold either the first 310 and/or the second metal sheet 312to the non-weldable sheet 314.

Accordingly, in other exemplary embodiments, it will be recognized thatthe sheets 310, 312 may not be joined along their respective edges(i.e., a more central portion of one or both sheets may be joined).However, in yet another exemplary embodiment, an edge of one or bothsheets 310, 312 may be directly over one or more holes 320.

When a vaporizing foil actuator 316 is used adjacent to the second metalsheet 312, the non-weldable sheet 314 operates as a spacer at the holeformed therein, and a portion of the second sheet 312 is deformed intothe hole 320, where it impacts the first metal sheet 310 to form a bond.

Similarly, such as shown in the example shown in FIGS. 8 and 9, whenmore than one hole 420 is provided in the non-weldable sheet 414 forjoining the first metal sheet 410 to the second metal sheet 412, eithera single elongated second metal sheet may be used or separate secondmetal sheets may be used. Furthermore, either a single first metal sheetor separate first metal sheets may be used. The exact arrangement will,of course, often be determined by the structural requirements of thesituation.

Any embodiment of the present invention may include any of the optionalor preferred features of the other embodiments of the present invention.The exemplary embodiments herein disclosed are not intended to beexhaustive or to unnecessarily limit the scope of the invention. Theexemplary embodiments were chosen and described in order to explain someof the principles of the present invention so that others skilled in theart may practice the invention. Having shown and described exemplaryembodiments of the present invention, those skilled in the art willrealize that many variations and modifications may be made to thedescribed invention. Many of those variations and modifications willprovide the same result and fall within the spirit of the claimedinvention. It is the intention, therefore, to limit the invention onlyas indicated by the scope of the claims.

What is claimed is:
 1. A method for joining dissimilar metals, saidmethod comprising the steps of: providing a first metal, a second metalthat is dissimilar to said first metal, and an intermediate bodycomprised of a carbon fiber composite and having at least one hole suchthat said first metal and said second metal are positioned on oppositesides of said intermediate body and over said at least one hole; anddriving at least a portion of said second metal into said hole such thatsaid second metal is welded to said first metal, and said intermediatebody is trapped between said first metal and said second metal.
 2. Themethod of claim 1 further comprising the step of providing a vaporizingfoil actuator that drives said portion of said second metal into saidhole such that said second metal is joined to said first metal.
 3. Themethod of claim 1, wherein said intermediate body has a plurality ofsaid holes such that said second metal is welded to said first metalthrough each of said holes.